In recent years, immunochromatographic strip type immunoassay has become increasingly important as a simple and easy in-vitro diagnostic kit or mobile diagnostic device for detecting an antigen in a sample solution by making use of the specific reactivity of an antibody. In particular, a pregnancy test kit is a familiar immunochromatographic device commercially available also as a nonprescription drug. Recently, simple and easy test tools based on the immunochromatographic method have been under development in order to determine the presence or absence of infection with a pathogen such as influenza virus or bacteria.
A test drug of the immunochromatographic method having an antibody labeled with an insoluble carrier has been used generally because it requires only a simple and easy operation and the test using it needs only a short time. However, in comparison with EIA, there has been a problem that it has generally low sensitivity and the line observed when the result is positive is not clear.
With a view to overcoming such a problem, a method of allowing sugar or a water-soluble high-molecular compound to exist in a developing solvent as in Patent Document 1 is proposed. However, even if this method is applied to the immunochromatographic method using an antibody labeled with an insoluble carrier, aggregation of the insoluble carrier may occur and a non-specific reaction may be caused. Problems such as low developing rate has not been able to be overcome (refer to Patent Document 1).
Therefore, there is an eager demand for the development of a test drug which does not cause aggregation of an insoluble carrier; does not cause a non-specific reaction; and has a high developing rate even if it is applied to the immunochromatographic method using an antibody labeled with an insoluble carrier.
For example, a method of easily analyzing a plurality of detection targets in a specimen by the membrane assay method using colored latex particles, wherein the colored latex particles have respectively different colors for two or more detection targets is proposed. The method is particularly effective for a detection object which is prone to false positive and more effective when two or more detection targets are selected from Influenza A virus, Influenza B virus, and RS virus (refer to Patent Document 2).
In a simple and easy testing method of a specimen by using the membrane assay method, a filtration method of a specimen sample capable of preventing a false positive result or clogging with keeping high sensitivity is provided (refer to Patent Document 3).
In Patent Documents 2 and 3, when the detection is conducted by the membrane assay method wherein a biological sample such as a swab from the nasal cavity or pharynx or an aspirate fluid from the nasal cavity is used, a suspension containing an MES buffer (Good's buffer), Triton X-100 (nonionic surfactant), protein such as bovine serum albumin or casein, and the like is used as a specimen suspension for suspending a specimen therein.
In Patent Document 4, in a testing method of respiratory infections by using a test tool based on the immunochromatographic method, a treatment solution containing a surfactant (NP40, or the like), a reducing agent (2-mercaptoethylamine hydrochloride, or the like), a thiocyanic acid compound, a chelating agent, a Good's buffers (PIPES, etc.), and the like is used as a specimen treatment solution for treating a specimen selected from a swab from the nasal cavity or pharynx and an aspirate fluid from the nasal cavity (Patent Document 4).
In the inventions described in Patent Documents 2 to 4, however, colored latex particles are used mainly as a labeling reagent and as a specimen treatment solution, conventionally employed ones are use since they do not take a particular attention to the specimen treatment solution.
Patent Document 5 takes an attention to a specimen treatment solution, which is used for the detection according to the membrane assay method. The treatment solution containing a nonionic surfactant (Nonion MN-811, or the like), bovine serum albumin, and a Tris-HCl buffer is used as a specimen treatment reagent composition to suppress a non-specific reaction (refer to Patent Document 5).
In Patent Document 6, as a specimen suspension composition, by using a treatment solution containing a nonionic surfactant (Triton X-100 or the like), a basic amino acid, a protein (bovine serum albumin, or the like) for stabilizing a substance to be measured, and a buffer (Tris-HCl, or the like) for keeping the pH at from 3 to 8, occurrence of a false positive result is prevented (refer to Patent Document 6).
However, the specimen treatment solution or developing solvent described in Patent Documents 2 to 6 has still the problem that it cannot fully suppress the aggregation of an insoluble carrier or induction of a non-specific reaction. Therefore, they are not fully satisfactory as a test drug having a high developing rate and there is an eager demand for further improvement.